1. Field of the Invention
This invention relates to a display device including a dual emission panel that emits light from the both surfaces of a substrate.
2. Related Art
In recent years, research on a light-emitting device including an electroluminescent element (hereinafter, EL element) manufactured as a self-luminous type light-emitting device has been intensified. The light-emitting device is also referred to as an organic EL display, or an organic light-emitting diode. Such light-emitting device has been attracted attention as a next generation display device such as a new generation cellular phone or a portable digital assistant for their characteristics of high reaction speed, low driving voltage, low power consumption, and the like.
An EL element including a layer containing an organic compound (hereinafter, EL layer) as a light-emitting layer has the structure in which the EL layer is interposed between an anode and a cathode. Upon applying current through the EL layer, holes and electrons are recombined to produce excitons in the EL layer (specifically, a light-emitting layer in the EL layer), and the excitons radiate energy while returning to the ground state. The energy is released by emitting light. Fluorescence that occurs from the singlet excited state back down to the ground state and phosphorescence that occurs from the triplet excited state back down to the ground state are obtainable from the EL element.
The foregoing EL layer is composed of single compound layer or a plurality of compound layers. For example, a hole injecting layer, a hole transporting layer, a light-emitting layer, an electron injecting layer, and an electron transporting layer are appropriately stacked to form the EL layer. Materials for forming the EL layer can be broadly divided into two categories, low molecular materials (monomer materials) and high molecular materials (polymer materials). The low molecular materials are formed into a film generally by a vapor deposition device.
Light from the EL layer is emitted out of a transparent anode or a transparent cathode. Hence, the EL layer can be used as a part of a light-emitting device. In general, ITO that is a transparent electrode is used for an anode in order to emit light out of the side of the anode. (For example, see Unexamined Patent Publication No. 5-234681.) However, a light-emitting device emitting light out of both an anode and a cathode, each of which is formed by a transparent film, has been developed and attracted attention in recent years. (For example, see SID 03 DIGEST pp. 104-107).
There is a problem in a light-emitting device emitting light out of both surfaces that an image on the surface and an image on the rear surface are different from each other (either image is mirror-reversed), and so erect images cannot be simultaneously seen on both surfaces.